Effect of thermo-mechanical cycles on the physico-chemical properties of poly(lactic acid)

Polylactic acid (PLA) has now become an economically viable commodity plastic in many industries. This raises the question of recyclability of industrial production waste and some packaging wastes as well. The evolution of rheological and mechanical properties of polymer with the number of recycling cycles up to seven was investigated. For PLA, only the tensile modulus remains constant with the thermo-mechanical cycles. In contrast, stress and strain at break, rheological factors and the modulus and hardness probed by nanoindentation decrease for PLA. This dramatic effect is ascribed to a large decrease in the molecular weight due to several different complex degradation processes which are discussed. The effect of two stabilizers is also assessed.